Electromagnetic techniques have been used to distinguish hydrocarbons and water. The methods generally rely on the contrast between the real part of the impedance signal from water and hydrocarbon, as water has a finite conductivity while hydrocarbon has a conductivity close to zero. However, using the real part of the impedance signal, it is not possible to determine the water saturation (fraction) of a hydrocarbon-water mixture from a single conductivity measurement as the conductivity of the water phase must be known independently. In particular, the conductivity of the water phase depends on salinity and can vary by more than a factor of ten.